Abstract: A storage box includes an upper cover integrally connected at a rear edge to a lower cover. The upper and the lower covers are provided along their peripheral edges with a recess and a flange, respectively, that engage with each other when the upper cover is closed onto the lower cover. Upper and lower marginal belts surrounding the recess and the flange, respectively, are provided with projections, so that a gap always exists between the two marginal belts to facilitate easy opening of the upper cover relative to the lower cover. The recess and the flange are provided with tongues that abut on each other to lock the upper cover to the lower cover but allow a fit clearance between the recess and the flange, so that the upper and the lower covers would not become stuck at the recess and the flange.